Saturday, June 11, 2022

Lander Update - 06/2022

I have been doing a bad job of updating progress. I had intended on once per week initially, but life.

Lately I have been focusing on finishing up avionics and firmware, and getting moving on some of the other significant mechanical work I have head of me. I finished assembling the TVC actuators and have tested them. I also built up a portion of the ground station terminal I will be using to operate and work with the vehicle.

Current CAD state of the vehicle -- I have not worked on this portion much lately. I have recently determined how I plan on mounting the COPVs, although the CAD below is missing the bottom support bucket and strap. Those will be hose clamps seated onto a rubber or TPU cup. I also bought a TIG welder for the garage, so I can get cracking on work without having to visit the machine shop space.

All avionics boots up and works fairly well. Some weird bugs to fix in the peripheral board firmware. The backup IMU I got on ebay is behaving weirdly, and the analog multiplexer does not seem to be multiplexing as I expect. But I have reason to believe neither of these is a PCB issue, either device or firmware level. I'm able to drive all the relays, but there is a weird timing bug where when everything boots up, the relay board sinks power into the IO expander and fires itself for 250ms prior to Teensy poweron. Not really fixable via pullups, I'm going to take a closer look at the register map to see if there is a persistent fix. These annoyances always crop up lol. Parsing 2x GPS packets seems to work fine.

Linear Actuators! I've finally finished building them up, and testing out the drive board software. I had to update the firmware on  a linux system, so that required me using a raspberry pi, and I felt like I should just build a ground station computer while I'm at it. Anyway, the bandwidth already is quite good. I plan on  trimming the stroke once I have a design figured out for the thrust structure/gimbal plate and the mounting points for the engine/chassis side.

I also designed a smaller, cheaper, and hopefully more stable linear actuator that I might use for the throttle valve actuator. It uses a 22mm carbon tube as the effector. It also has some 3D printed parts that I'll need to sus out in PETG. Most other components are laser cut stainless steel. I still dislike the mounting situation..

Here is the prototypical grounds station in a pelican case. The portable monitor is used from ebay for $80 and is a super great deal. Basically an XPS15 screen you can just bolt down anywhere. I designed 3D printable adhesive bolt down brackets for it, with heat threaded inserts. Worked out quite well. The bottom of the case has a bunch of extra hardware you can tap into while out in the field. I will print some standoffs and laser cut an aluminum recess plate for the keyboard + other stuff to go onto. Work in progress!

I still need a good antenna solution...

I also made some custom battery packs for the valve power supply. These will be dedicated to firing valves, and have all the right electrical isolation to separate systems.

The look sketchy, but I've done worse...

Still so much work to do.
  • Finish up small issues with avionics 
  • Get the ground station network piping figured out and update FSW, and start writing ground procedures for polarity testing.
  • Finish welding the feedheads and hydro test the tanks! Finally! Please!
  • Take what I learned and apply it to the lox tank, mount that to the airframe
  • Mount my COPV
  • Hold a design review w some of my friends for the P&ID plumbing diagrams for all fluid systems
    •  This will also help me figure out much more to spend on components.. I have most of the regs/valves and a bunch of fittings. but no tubing lol
  • Design and build the throttle valve
  • Finish thrust structure and gimbal plate design
  • FSW and GNC Sim work (Julia Lang?)
  • Engine design!!!!
  • Countless other things I have on my white board

Here's a great picture I took the other week.

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